Method for producing seamless tubes with small diameters

ABSTRACT

Method for producing seamless tubes of small diameter. The starting tube is subjected to at least one initial cold drawing over an interior tool, decreasing the diameter and the wall thickness of the tube so that the interior tube surface is brought into complete contact with the interior tool. The tube is then subjected to stretch reducing and to final cold drawing over an interior tool.

United States Patent Petersen et al.

[451 May 9, 1972 [54] METHOD FOR PRODUCING SEAMLESS TUBES WITH SMALLDIAMETERS [72] Inventors: Ulrich Petersen, Dusseldorf; Ernst Von Chiari,Solingen; Wilhelm Brutsch, Remscheid, all of Germany MannesmannAktiengesellschaft, Dusseldorf, Germany [73] Assignee:

[22] Filed: Oct. 29, 1969 211 Appl. No.: 872,373

US. Cl ..72/206, 72/283, 72/370 ..B21b 23/00 Field of Search ..72/206,274, 278, 283, 367,

Primary Examiner-Lowell A. Larson Attorney'Nolte & Nolte [57] ABSTRACTMethod for producing seamless tubes of small diameter. The starting tubeis subjected to at least one initial cold drawing over an interior tool,decreasing the diameter and the wall thickness of the tube so that theinterior tube surface is brought into complete contact with the interiortool. The tube is then subjected to stretch reducing and to final colddrawing over an interior tool.

3 Claims, No Drawings METHOD FOR PRODUCING SEAMLESS TUBES WITH SMALLDIAMETERS The present invention relates to a method for producingseamless tubes with small diameters. The object resides in manufacturingtubes economically with improved interior surfaces.

In producing seamless tubes with small diameters it has been the generalpractice to start with tubes with a diameter of about 90 to 150 mm andto use stretch reducing. When it is desired to obtain even smaller tubediameters than can be achieved by stretch reducing or if there isdesired the quality of cold drawn tubes then the tubes are subsequentlysubjected to several cold drawings. Such method is the more economicalthe greater the diameter of the starting tube is, and the fewer colddrawing steps are performed.

This is in contrast to technological experience, according to which theinterior surface as a result of radial shiftings of the crystallites inrespect to each other becomes rougher by stretch reducing and the numberof subsequent cold drawing steps must be increased. It can also resultthat the roughness formed cannot be remedied satisfactorily by colddrawing.

The present invention is a further development of the described methodsfor producing seamless tubes with small diameter by stretch reducing andsubsequent cold drawing and is characterized in that the starting tubebefore stretch reducing is subjected to at least one cold drawing withinterior tool. By such preceding cold drawing the diameter and the wallthickness are to be decreased in such a degree that the interior tubesurface is brought into complete contact with the interior tool.

The decrease of diameter, required for this purpose, amounts to only afew millimeters and can be easily obtained by shaping technology. Inthis connection, drawing with floating plug is preferred, because thesame can be easily performed and allows the processing of considerabletube lengths. At least for smaller diameters of the starting tubes therecan be used the plug rod technique.

lt is essential that the tool smoothes and compacts the interior tubesurface over the complete tube length. The crystallites directlyadjacent to the interior tube surface thereby are left easily shiftableradially in respect to each other and the interior tube surface remainssmoother upon stretch reducing. In addition to this quality improvementof the tubes the drawing work is decreased in that the initial colddrawing of the tube replaces several drawings which must otherwisefollow the stretch reducing.

According to the present invention it is further proposed that theinitially cold drawn tube is heated so as to effect the stretch reducingwithout forming of scale on the smoothed interior tube surface.Generally it is sufficient to provide rapid tube heating as is achievede.g. by electric heating with inductive or conductive current transfer.It is possible to use a protective gas with which the tubes are filledduring the heating up.

It is preferred to restrict the diameter decrease effected by stretchreducing, both as to its total value and per rolling mill. This appliesparticularly to tubes heavier than those with normal wall thickness.According to such proposal a tube with e.g. 100 mm exterior diameterafter initial cold drawing is to be reduced to no less than about 25 mm,on all applied rolling mills of an ordinary stretch reducing plant.

The production of a cold drawn precision tube with a diameter of 22 mmand a wall thickness of 2 mm is accordingly performed e.g. as follows:

The starting tube has an exterior diameter of 108 mm and a wallthickness of 4.0 mm; it is easier to obtain such dimensions by precedingwork than to use a tube of the same diameter and a normal wallthickness.

In the initial cold drawing the tube is drawn over a plug with adiameter of mm to an exterior diameter of 102 mm and a wall thickness of3.5 mm.

When introduced into stretch reducing plant the tube is heated by meansof an induction coil to about 950 C, is reduced in e.g. 20 rolling millsto a diameter of 25 mm and a wall thickness of 2.5 mm, and is thendischarged.

After the cooling and the usual pre-treatment the tubes are thenprocessed by a single cold drawing over a plug with a diameter of 18 mmto the desired final dimensions.

What we claim is:

1. Method for producing seamless tubes of small diameter comprising thesteps of initially subjecting a tube of larger diameter to at least onecold drawing over an interior to decrease said larger diameter so thatthe interior tube surface is brought into complete contact with theinterior tool;

then stretch reducing the cold drawn tube; and

cold drawing the stretch reduced tube to establish the small diameter.

2. Method according to claim 1 wherein the stretch reducing includesheating the tube so as to avoid formation of scale.

3. Method according to claim 1 wherein the stretch reducing is effectedwith relatively small decreases of the tube diameter, for exampledecreasing a tube of mm exterior diameter to no less than about 25 mm.in the stretch reducing operation.

Patent No. Dated May 97 Inventor(s) Ulrich Petersen, 8.1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Page 1, column 2, line 35 (line 3 of claim 1), interior to" should read"interior tool to" Signed and "sealed this 8th day of August 1972.

(SEAL) Attest:

EDWARD M.FLETCHEJR,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents DRM PO-1 OSO (10-69)

1. Method for producing seamless tubes of small diameter comprising thesteps of initially subjecting a tube of larger diameter to at least onecold drawing over an interior to decrease said larger diameter so thatthe interior tube surface is brought into complete contact with theinterior tool; then stretch reducing the cold drawn tube; and colddrawing the stretch reduced tube to establish the small diameter. 2.Method according to claim 1 wherein the stretch reducing includesheating the tube so as to avoid formation of scale.
 3. Method accordingto claim 1 wherein the stretch reducing is effected with relativelysmall decreases of the tube diameter, for example decreasing a tube of100 mm exterior diameter to no less than about 25 mm. in the stretchreducing operation.